In the current communication system, one cell may cover multiple areas. Two solutions in the existing art regarding the one cell covering multiple areas are presented as below.
Solution 1: A Base Station and a repeater enable one cell to cover multiple areas, as shown in FIG. 1 and FIG. 2.
In FIG. 1, three areas, namely, area C, building A, and building B belong to the same cell. A local end 1 and a remote end 1 constitute a repeater, and a local end 2 and a remote end 2 constitute another repeater. Therefore, one Base Station and two repeaters accomplish coverage for three areas (A, B, and C) in a cell. Areas A, B, and C belong to one cell, and the cell corresponds to one Radio Frequency (RF) module in the Base Station. The remote end 1 includes an RF module, and the remote end 2 includes an RF module. Therefore, three RF modules are required for one cell to cover multiple areas in FIG. 1.
In FIG. 2, floors 1-10 and floors 11-20 belong to the same cell. A local end 1 and a remote end 1 constitute a repeater, and the repeater covers higher floors 11-20. A local end 2 and a remote end 2 constitute another repeater, and this repeater covers lower floors 1-10. Therefore, one Base Station and two repeaters accomplish coverage for two areas (higher-floor area, and lower-floor area) in a cell. The higher-floor area and the lower-floor area belong to one cell, and the cell corresponds to one RF module in the Base Station. The remote end 1 includes an RF module, and the remote end 2 includes an RF module. Therefore, three RF modules are required for one cell to cover multiple areas in FIG. 2.
Solution 2: A Baseband Unit (BBU) and a Remote Radio Unit (RRU) enable one cell to cover multiple areas, as shown in FIG. 3.
In FIG. 3, lower floors 1-10 and higher floors 11-20 belong to the same cell. RRU 1 covers higher floors 11-20, RRU 2 covers lower floors 1-10, and RRU 1 and RRU 2 are connected with the BBU in the Base Station through a Digital Combiner and Divider unit. Therefore, two remote RF modules and a digital combiner and divider unit accomplish coverage for both the higher-floor area and the lower-floor area in a cell.
In the process of implementing the present invention, the inventor finds at least the following two problems in solution 1 in the conventional art.
Problem 1: The system capacity is decreased. The repeater raises the noise floor of the Base Station. The rise of the noise floor interferes with all users in the same cell, and increases interference to neighboring cells. Moreover, in the uplink direction, the RF module in the Base Station receives signals of User Equipment (UE) in multiple coverage areas simultaneously, and the uplink signals lead to interference between different areas; in the downlink direction, the UE in a coverage area receives the downlink signals sent to the UE in other coverage areas while receiving the downlink signals sent to this UE, and the downlink signals lead to interference between different areas. Such factors affect the system capacity.
Problem 2: If multiple areas in a cell need to be split into cells, additional RF modules need to be set in the Base Station, and re-cabling is required for the RF modules and the local end in the Base Station. Therefore, the cell splitting is costly and difficult.
In the process of implementing the present invention, the inventor finds at least the following two problems in solution 2 in the conventional art.
Problem 1: Interference exists between users in a cell. For example, in the uplink direction, the signals of UE 1 in the higher-floor area are gathered by the digital combiner to the BBU, and lead to interference to UE 2 in the lower-floor area.
Problem 2: The downlink capacity is decreased. For example, in the downlink direction, if only UE 2 in the lower-floor area is in a conversation, the transmitting power of RRU 2 is 1 w. However, due to principles of the digital combiner and divider unit, the transmitting power of RRU 1 is 1 w too. For RRU 1, such power is wasted, and is equivalent to decrease of the downlink capacity. Besides, if UE 1 and UE 2 in different areas talk with each other, according to the digital combiner and divider unit, RRU 1 sends downlink signals to both UE 1 and UE 2 simultaneously. UE 1 receives not only the required signals, but also the downlink signals sent by RRU 1 to UE 2, which are interference to UE 1 and further decrease the downlink capacity.